Satan is described in the NT as being a deceiver. That's his primary tactic. Attributing falling sick because you didn't pray yesterday, natural disasters, or viruses like Covid, human mistakes like forgetfulness, mental illness, or even theft are mistaken notions. What Satan does is deceive people about spiritual truth. Satan is known in the NT as a liar and deceiver—that's what the work of the devil is.

I would like you to elaborate as much as possible because I'm curious about where you draw the line from something being the work of the devil, a coincidence like you didn't pray yesterday and today you suddenly fell sick, a natural disaster or calamity like covid, human mistakes like forgetfulness or intentional actions like theft. Is the devil involved in any of these examples or all of them?

For context's sake, while I was a Christian I was taught by authority figures that all sin starts with the devil but then other things that cause pain or distress are also the work of the devil like illnesses and mental problems.

How do you know what is and isn't the work of the devil? Does the devil do anything?